With the rise of electronic stereoscopy in the last two decades, different formats have been used to produce stereoscopic images. The subject is discussed in Lipton's paper in the 1997 SPIE Proceedings Stereoscopic Displays and Virtual Reality Systems IV volume 3012 entitled Stereovision Formats For Video And Computer Graphics. The formats sometimes involve means for producing a sequence of fields, and require selection devices employing electro-optical shutters for occluding and passing fields. In this way each eye of the viewer sees its appropriate perspective view. In some cases, the parts of the electro-optical system are distributed, covering the monitor with a modulator and passive eyewear at the eyes of the beholder.
Many formats come down to the same thing—an alternating sequence of left and right fields. Also common is page flipping, which requires a stereo-ready video graphics board that can accept the proper calls from, typically, an open GL application, which can then signify or index the appropriate field so that each eye sees its appropriate image. Other means have been created in addition to the page-flipping mode, which is one that is common on UNIX workstations but less common on Windows workstations. The above/below format (sometimes called sync doubling) invented by Lipton et al. is a format that is not board dependent, as described in U.S. Pat. No. 4,523,226, entitled Stereoscopic Television System. This is a commonly used technique, but it does not allow stereoscopic windows to be produced, and it has other disadvantages, although it will function without regard to the video board used.
Another approach, the interlace approach, uses alternating fields running at the usual repetition rate, for example, 60 or 70 fields per second, and thereby produces a flickering image. This is a method that has been used for video systems, and it can be used for DVD encoding of stereo images as described in co-pending and commonly assigned U.S. application Ser. No. 10/150,595 entitled Plano-Stereoscopic DVD Movies.
Another method, the interline method, writes left and right lines on the same video field and squelches them using a “dongle” which connects to the VGA video port of the computer. In this way, left and right images are passed at the discretion of the dongle, which alternately squelches left and right lines.
There are some people (children especially) who are perfectly content with the redoubtable anaglyph which uses color encoding of the left and right images. This method was described almost a century-and-a-half ago and is most often used with red and green or red and blue filters. There are two major variants. One is a polychrome anaglyph that attempts to give some semblance of color. The other is a more traditional monochrome anaglyph that is probably more pleasant for most people to look at, but lacks the pizzazz of having a color effect.
CRT monitors allow for field-sequential or alternate-field stereoscopic displays (described above), whereas liquid crystal displays do not because of image lag. In order to see a stereo image on a liquid crystal display, the anaglyph is required. Another method for use on such an uncooperative monitor would be to place the left and right images side by side, in which case they can be free viewed (no selection device) by people who have the knack. There's also the possibility of using lorgnettes, or eyewear that have prisms in them, so that the images can be converged for the observer.
StereoGraphics Corp. of San Rafael, Calif., sells SynthaGram® autostereoscopic monitors which use a special multi-tile format; yet another format variation to be reckoned with.
This disclosure addresses material that is produced in one format and then disseminated to users without knowledge of the user's hardware or its ability to play back the image. For example, an above-and-below formatted image might be sent to someone who has a laptop with a built-in liquid crystal display screen. Can he/she view the stereo image? Generally no—unless, for example, the image can be transformed into an anaglyph which is independent of the display's ability to refresh at a given rate without fields blending into each other.
In general, there are a wide variety of formats and many kinds of PC's and monitors in use and not a high degree of certainty that a user will be able to view stereoscopically in the format received.
In addition, there are people who would like to see stereoscopic images but who have planar stills or movies to look at. These people might enjoy seeing a stereoscopic image for the novelty's sake. Even if it isn't a true stereoscopic image, it might be pleasant, in some circumstances, to provide an ersatz stereoscopic image.